Device for producing an oscillator signal

ABSTRACT

The invention relates to a device and a method for producing an oscillator signal based on a base signal. Said oscillator signal is actively constructed by an oscillator. The oscillator can be quasi-phase-coherently excited by the base signal.

[0001] The invention relates to a device according to the preamble ofclaim 1 and to a method according to the preamble of claim 15.

[0002] In the field of radio frequency engineering, it is advantageousand usual to evaluate radio-frequency microwave signals not directly butin relation to a reference signal. This relates, for example, to systemsfor data transmission in which a transmitter, which will be called basestation in the text which follows, sends a base signal and this basesignal is compared with a reference signal which is generated in areceiver, and processed further in a receiving station. Thus, forexample, mixers or demodulators are frequently used by means of whichthe received signal is down converted into a band of in most cases lowerfrequency by means of a reference signal. Since, as a rule, theradio-frequency base signal is only used as a carrier onto which amodulation or information of lower frequency is impressed, it ispossible, for example, to suppress the carrier by means of thisconversion and thus to derive the information contained in themodulation in a simpler manner.

[0003] In so-called transponder, transceiver, backscatter or also radarsystems, a base signal, which is also called an interrogating signal inthis case, is sent by the base station to the transponder or to areflector and from here is transmitted back to the base station as aresponse signal, possibly modified, and is there received again. In mostcases, the evaluation in the base station then takes place in such amanner that the transmitted base signal itself is used as the referencesignal by means of which the response signal is evaluated in order toderive in this way, for example, information added in the transponder ora sensor information item such as, e.g. the delay of the signal and thusthe length of the transmission link.

[0004] In such systems it is also usual that in the transponder, thereceived base signal is also processed with a reference signal before aresponse signal is sent back or, respectively, the reference signalitself, possibly with a characteristic information item added, is sentback to the base station. Such transponders with their own source forsending back the response will be called active transponders or activebackscatter devices in the text which follows. By comparison, systemswithout their own source, that is to say those which only send back thebase signal, possibly modified and amplified, are called passive.

[0005] In all cases it is advantageous if the reference signal isrelated as precisely as possible to the base signal or to its carrierwith respect to frequency and phase. The more precise this frequency andphase relation, the simpler and/or the more interference-proof is themanner in which the information contained in the base signal or in theresponse signal can be derived. If the base signal is sent by a basestation and received and processed further in the manner described in aspatially distant receiving station, this desired frequency and phaserelation is not readily given since both signals, that is to say thebase signal generated in the base station and the reference signalgenerated in the receiving station come from different sources.

[0006] For the above reasons, therefore, it is of general interest tocouple the reference signal to the base signal in some way. For thispurpose, different methods and arrangements are normally used. A simplefrequency relation can be implemented by using oscillators with highfrequency stability in the transmitter and in the receiver. However, anunknown residual frequency offset will always still remain in this casedue to, for example, temperature or aging drift. For this reason, thephases of the two sources cannot have a fixed relation. More elaboratearrangements have means which are suitable for determining the residualfrequency offset and/or the residual phase offset. On the basis of thedeviation quantities determined, the base signal source or the referencesignal source can then be controlled. For this purpose, differentfrequency and phase control loops are used. Similarly, additionalinterrogating signals or quantities can be formed from the residualsignals, which are utilized for further signal processing.

[0007] In the field of communications technology, a variety of methodsfor recovering a carrier are commonly used. The synchronization ofoscillators by means of so-called “injection locking” also belongs tothe prior art, see, for example, M. Wollitzer, J. Buechler and E. Bibbl,“Supramonic Injection Locking Slot Oscillators”, Electronics Letters,1993, Vol. 29, No. 22, pages 1958 to 1959. In this case, the oscillatorto be controlled is in most cases locked onto a strong stableoscillator. The locking is usually done in CW (Continuous-Wave) mode andsubharmonic oscillation modes can also be used for the application. Ingeneral, controlling the reference source on the basis of aninterrogating signal becomes susceptible to interference andcomplicated, in particular, if the receiving station is operating notonly as a pure receiver but sends back the interrogating signal,possibly provided with an additional information item, as responsesignal as a transponder, transceiver or active backscatterer. In thiscase, so-called multiplexing methods must be used for ensuring that theresponse signal which, as a rule, has a much higher amplitude than theinterrogating signal, is not cross-coupled onto the receiving branchand/or onto the control loop. For example, time-division,frequency-division or polarization-division multiplexing methods arenormally used. In the case of time-division multiplex, the receivingstation first responds to the interrogating signal with a skew. Thegreater the skew and/or the higher the microwave frequency, the morecomplicated it is to maintain phase coherence between the source of thebase station and that of the transponder. Even extremely small relativefrequency deviations of the sources which cannot be avoided due to drifteffects, phase noise and control inaccuracies lead to an undefined phaserelationship of the sources within a relatively short time in the caseof signals of very high frequency. In the case of frequency-divisionmultiplex, the interrogating signal is converted to another frequency inthe transponder before it is sent back. This requires dividers,multipliers or additional signal sources and mixers and possibly anumber of antennas which are tuned to the respective frequencies. Inpractice, the principle of frequency multiplication or division alsofrequently fails because of the radio licensing since, as a rule, thefrequencies of the released bands do not have an integral-numbereddividing ratio.

[0008] If it is intended to determine the distance or a change indistance between a base station and a transponder, for example inaccordance with the principle of the Doppler or frequency-modulationradar, there are even further demands on the phase relation between theinterrogating signal transmitted and the response signal sent back. Inthis case, the phase of the response signal sent back by the transpondermust exactly correspond to the phase of the signal received in thetransponder, if necessary apart from a constant offset, so that theinterrogating signal sent by the base station and the response signalreceived by it after having been sent back by the transponder have aphase difference which is proportional to the distance between the basestation and the transponder but otherwise does not change with time.

[0009] Since, in practice, it is only with great difficulty that thisphase coherence between two radio-frequency sources can be achieved,passive backscattering transponders which do not have their own signalsources but only reflect back the interrogating signal, possiblyamplified, are currently used in most cases. Such systems are described,for example, in Klaus Finkenzeller “RFID-Handbuch” [RFID Manual], secondedition, Carl Hanser Verlag, Munich 1999. The disadvantageous factor insuch passive backscattering systems is that the transmitted signal musttravel along the path from the base station to the transponder as aninterrogating signal and back as a response signal and, therefore, thesignal/noise ratio of the entire transmission link decreases inproportion to the fourth power of the distance. Because the free-fieldloss greatly increases with frequency, it is scarcely possible toimplement, in particular, passive backscattering transponders of veryhigh frequency in the Gigahertz range with a satisfactory signal/noiseratio. This is unsatisfactory, in particular, because, in principle,because of the great bandwidth available, Gigahertz systems can be veryadvantageously used both for range finding and for fast datatransmission.

[0010] In addition, there are systems in which the base signal is notsimply reflected and possibly also amplified but in which the responsesignal is actively constructed on the basis of the base signal, e.g. bymeans of an active oscillator. For the active design, the relevantparameters are extracted from the base signal and the oscillator signalis generated independently on the basis of the extracted parameters. Itrepresents a reconstruction of the base signal inasmuch as itcorresponds to it in the required parameters. Beyond the merereconstruction, other signal components can also be impressed on theoscillator signal in order to transmit, e.g. additional information.

[0011] If a new signal is generated in the transponder in this manner onthe basis of a received signal by means of an active oscillator asindependent source, the path from the base station to the transponder isin each case only traveled once by the signal from a source. In thiscase, the signal/noise ratio is only inversely proportional to the powerof two of the distance. To this is added that other attenuations andlosses on the transmission path act on the signal only once and nottwice. The signal/noise ratio is, therefore, particularly in the case ofgreater distances and/or high frequencies, better by orders of magnitudethan in the case of passive backscattering systems in which the signalmust travel to and fro on the path from the base station to thetransponder.

[0012] A more complex transponder system in which the transponderbackscatterer operates with its own source is specified in German patentapplication 19946168.6. This system operates in time-division multiplexand bypasses some of the disadvantages shown by means of a clever choiceof modulation and control. However, it is relatively elaborate. It usesthe methods which are used in GPS (Global Positioning System). Othersystems are mentioned, for example, in U.S. Pat. No. 5,453,748 or in C.Luxey, J M. Laheurte “A Retrodirective Transponder with PolarizationDuplexing for Dedicated short-range Communications”, IEEE Transactionson Microwaves Theory and Technics, Vol. 47, No. 9, pages 1910 to 1915,or in M. M. Kaleja et al., “Imaging RFID System at 24 Gigahertz forObject Localization, 1999 IEEE MTT-S International Microwave Symposium,Anna Hein, USA, Vol. 4, pages 1497 to 1500.

[0013] It is the object of the invention to demonstrate a particularlysimple method by means of which it is possible to lock a signal sourcein the radio-frequency range quasi-phase-coherently to a referencesignal. Quasi-phase-coherent means that the phase difference between thebase signal and the reference signal generated is small, the term smallbeing meant with respect to the intended communication or measuringtask. As limit for a small phase deviation, for example, the value π/10,that is to say approx. 20° is frequently used. Such signals having onlysmall phase deviations will be called quasi-phase-coherent in the textwhich follows and the time interval within which this coherence existsthe duration of coherence.

[0014] The said object is achieved by a device having the features ofclaim 1 and by a method having the features of claim 15.

[0015] The essential factor in this is that it is not only theoscillations of the active oscillator which are quasi-phase-coherentwith respect to the base signal but the excitation of that activeoscillator is also quasi-phase-coherent. Whereas the active oscillatorin devices and methods of the prior art is excited by thermal noise andits oscillations are made quasi-phase-coherent only later by means of anelaborate control process and lock-in, the oscillator in the subjectmatter of the application is already excited quasi-phase-coherently bythe base signal, that is to say its oscillation build-up is alreadyquasi-phase-coherent and the phase coherence is thus establishedvirtually automatically. The oscillation of the oscillator can thus beinitialized quasi-phase-coherently or, respectively, isquasi-phase-coherently initialized.

[0016] The basic concept of the invention consists in that an oscillatorin its basic state is in an unstable equilibrium and, when it isswitched on, must first be excited into oscillation by being suppliedwith external energy of whatever type. It is only after this initialexcitation that the feedback with which the oscillation is maintainedbecomes active. Usually, for example, the thermal noise is used for suchan initialization of an oscillating circuit. This means that anoscillator starts to oscillate with a random phase and amplitude andthen oscillates at its frequency predetermined by its resonant circuit.If, however, an external excitation signal is injected into theoscillator on switch-on, the frequency of which is within the bandwidthof the resonant circuit and the power of which is significantly abovethe noise power, the oscillator will start to oscillate not randomly butsynchronously with the phase of the exciting base signal. Thisquasi-phase-coherence remains in existence at least for a time dependingon the frequency difference between the exciting base signal and theoscillator signal and in dependence on the phase noise of the twooscillators.

[0017] The difference of the present invention with respect to the knownpassive devices and methods consists in the use of an active oscillator.Thus, the base signal is not simply reflected back but before it is sentback, an independent quasi-phase-coherent source is used to activelyconstruct an oscillator signal almost free of noise. The systemaccording to the invention thus has a significantly greater range thanpassive systems of the prior art whilst its operation is otherwisesimilar.

[0018] The oscillator signal of the active oscillator can be used asresponse signal or reference signal, depending on whether this isunidirectional or bidirectional signal transmission.

[0019] Furthermore, control loops for any carrier recovery can beomitted in the device according to the invention. In transponderarrangements, a particular advantage consists in that no time-division,frequency-division or polarization-division multiplex is necessary sincethe base signal and the oscillator signal do not influence each other oronly influence each other in the desired manner at the beginning of thebuilding-up process and after that are quasi-phase-coherentindependently of one another.

[0020] It is advantageous if the device has a switching means forswitching the quasi-phase-coherent exciteability of the activeoscillator. This switching means is used for placing the activeoscillator into a state from which, excited by the base signal, it canbuild up quasi-phase-coherently to the base signal oscillation.

[0021] To switch the exciteability, it is not absolutely necessary toswitch the oscillations completely on and off. If, for example, theactive oscillator can oscillate in different modes, a second mode cansimply be switched while the first one continues to oscillate. Even withonly one mode, the oscillation does not need to be switched offcompletely but, as a rule, attenuation is sufficient so that the basesignal is sufficient for the next quasi-phase-coherent excitation.

[0022] If the exciteability of the active oscillator is switched onagain after the coherence duration, the quasi-phase-coherence remains inexistence over a relatively long period.

[0023] If, in further development, the quasi-phase-coherentexciteability of the active oscillator is repeated, thequasi-phase-coherence remains in existence even over relatively longperiods. This can be achieved by the switching means being constructedin such a manner that it switches the active oscillator with apredetermined sequence. This sequence can be a complex sequence which byitself is a carrier of information, or also a cyclic repetition in theform of a clock rate.

[0024] The duration between successive switching of the exciteabilitypreferably approximately corresponds to the coherence duration. However,a faster switching is also possible without the quasi-coherence betweenbase and oscillator signal being lost. If, on the other hand, thequasi-phase-coherence is only necessary in particular time intervals,the duration between two successive switching-on processes of theexciteability can also be selected to be longer than the coherenceduration. In the case of a cyclic sequence in the form of a clock, thecycles must be correspondingly adapted to the coherence duration.

[0025] If the switching of the active oscillator is repeated and theactive oscillator repeatedly starts to oscillate quasi-phase-coherentlywith respect to the base signal, the oscillator signal generated by theactive oscillator can be considered to be a sampled duplicate of thebase signal. If the sampling theorem is adhered to, a signal iscompletely described by its samples. The off duration of the activeoscillator is suitably not much longer than the on duration, that is tosay not much longer than the coherence duration. Maintaining thesampling theorem is thus inherent because of the coherence condition.According to the sampling theorem, the phase difference between twosampling points must be less than 180°. This condition is lessrestrictive than the quasi-coherence condition. In consequence, from thepoint of view of information technology, the signal of the switchedoscillator must be considered as a copy of the reference signal, inspite of the switching process, and carries the complete information ofthe former.

[0026] The exciteability of the active oscillator can be switched in arelatively simple way by switching the oscillator itself. Accordingly,the device can have a means for switching the active oscillator on andoff. To switch the oscillator, any means which has the effect that theoscillating condition of the oscillator is given or, respectively, nolonger given is suitable. Thus, e.g. in the oscillating circuit, thegain can be switched off, losses or delays (phases) can be changed orthe feedback branch can be opened.

[0027] Apart from its fundamental mode, the active oscillator can alsobe excited quasi-phase-coherently in one of its subharmonic modes ofoscillation. In this context, the fundamental mode or a subharmonic modeof oscillation of the base signal can be used for the excitation.

[0028] If the device is used for identification as ID tag or forcommunication, the coding can be done, for example by means of thesequence of switching the exciteability of the oscillator, particularlyby the switching means having a clock rate in accordance with thedesired coding. As an alternative, the device has an additionalmodulation unit by means of which the quasi-phase-coherent signal ismodulated before it is sent back.

[0029] As already explained, the coherence duration depends on thefrequency difference between base and oscillator signal. The moreprecisely the frequencies are matched, the longer the phases of thesignals are almost identical. To increase the coherence duration, as aresult of which the clock rate of the switching means can also be keptlow, it may be advantageous to provide means which are suitable foradaptively adapting the oscillator frequency to the frequency of thebase signal.

[0030] When selecting the active oscillator, attention must be paid tothe fact that its building-up time should be short compared with thecoherence duration. For this reason, the quality factor of theoscillator selected should not be too large. However, the quality factorshould also not be too low since low-quality oscillators usually havehigh phase noise.

[0031] In an arrangement with a device for generating an oscillatorsignal and with a base station in which the base signal is generated andby which it is sent to the device, the oscillator signal can be sentback to the base station by the device as response signal to the basesignal.

[0032] In an application in which the device communicates with a basestation via base and oscillator signals as interrogating and responsesignals, the base station preferably has a band-pass filter, the centerfrequency of which approximately corresponds to the clock rate of theswitching means, and/or means in order to eliminate the influence of theclock rate. Such means can be an additional mixer or a rectifier and alow-pass filter.

[0033] Further advantageous features essential to the invention areobtained from the description of exemplary embodiments, referring to thedrawings, in which:

[0034]FIG. 1 shows a device with oscillator and switching means,

[0035]FIG. 2 shows an arrangement with base station and transponder,

[0036]FIG. 3 shows a device with phase shifter for use as an ID tag,

[0037]FIG. 4 shows a device with a variably-frequency oscillator, and

[0038]FIG. 5 shows a device with amplifier and resonator.

[0039]FIG. 1 shows the basic elements of the device. A more or lesslarge proportion of a base signal A is coupled into an oscillator 2 viaan input 1. For the examples shown, an electrical base signal andoscillator signal are used as a basis. However, the invention can alsobe implemented for optical, acoustic or other signals. The base signal Aquasi-phase-coherently excites the oscillator 2 into oscillations, as aresult of which the oscillator generates the signal B. The signal B iscoupled out of the oscillator and delivered via an output 3. The input 1for the base signal A and the output 4 for the oscillator signal B canbe wholly or partially identical. However, they can also be implementedseparately of one another.

[0040] The oscillator 2 is cyclically switched on and off by means of aswitching means 4 for clock control. Its quasi-phase-coherentexciteability is also switched by the switching-on and off.

[0041] The oscillator 2 is constructed in such a manner that, on the onehand, it is not excited into oscillation by thermal noise but, on theother hand, the base signal A coupled into it is sufficient for excitingquasi-phase-coherent oscillations with respect to the base signal A.

[0042]FIG. 2 shows the arrangement of a transponder/backscatteringsystem. The base signal A of the base station 6 is generated by means ofa base station oscillator 7 and sent out via an antenna 8 of the basestation 6. The base signal A of the base station 6 is received asinterrogating signal by means of the antenna 5.

[0043] The switched oscillator 2 is excited quasi-coherently withrespect to the base signal A in the manner described above andoscillates in order to generate the oscillator signal B. The oscillatorsignal B is sent back as response signal via the antenna 5 of thetransponder 9 and to the antenna 8 of the base station 6.

[0044] The oscillator signal B is here separated from the base signal Avia a directional coupler 10 and mixed with a part of the signal fromthe base station oscillator 7 in a mixer 11. A filter 12 is used forsuppressing the mixture components which are not of interest. Thisfilter is preferably designed as a band-pass filter, the centerfrequency corresponding to the clock rate of the switching means 4. Thearrangement presented can be used both for the purpose of communicationor identification and for determining the distance or change in distancebetween the base station 6 and the transponder 9.

[0045] If the system is used for range finding, the base station 6preferably contains other elements such as, for example, an additionalmixer or a rectifier and a low-pass filter by means of which theinfluence of the clock rate is eliminated. However, the mixed signal canalso be evaluated directly by means of suitable spectrum analysis,taking into consideration the influence of the clock rate.

[0046] It is also advantageous for range finding if the base stationoscillator 7 is constructed as a variable-frequency oscillator, e.g. asVCO (Voltage Controlled Oscillator) so that the base signal A can assumemore than one frequency value. In principle, all designs as in aconventional backscatterer are conceivable as are also listed in Germanpatent application 19946161.9, reference to the complete content ofwhich is herewith made. The difference of the present invention withrespect to the known method consists in the type of transponder, namelythat the base signal, the signal level of which is already distinctlyattenuated by the transmission from the base station to the transponder,is not simply reflected but is generated in an actively constructedmanner, almost free of noise, with a separate quasi-phase-coherentsource and is then sent back with the full level of the source. Whilstotherwise operating similarly, the system according to the invention,therefore, has a significantly greater range or, respectively, asignificantly higher signal/noise ratio than the system according to theprior art.

[0047] If the transponder 9 is used for identification as ID tag or forcommunication, the coding can be done, for example, by means of theclock rate of the switching means 4 and/or by means of an additionalmodulation unit by means of which the quasi-phase-coherent oscillatorsignal, before being sent back, is modulated. The type of modulation cancorrespond to the general prior art which has already been referred toabove. Due to the quasi-phase-coherence of the two carrier signals, thatis to say of the base signal A and the oscillator signal B, thedemodulation in the base station 6 can be done simply and in aninterference-proof manner. In addition, the abovementioned advantagescompared with normal backscattering ID systems for greater range areobtained. Control loops for any carrier recovery can be omitted in thearrangement according to the invention.

[0048] Using the arrangement, the coding of an ID tag can be achieved,for instance by means of phase modulation. FIG. 3 shows a possibleembodiment. Compared with the preceding transponder circuits, the systemshown has only been extended by a modulator/phase shifter 13. Dependingon the code value C, the quasi-phase-coherent oscillator signal isdelayed by a particular phase value. In binary coding, this is, forexample, by 90° or 180° in the case of the code value 1 and by 0° in thecase of the code value 0. Amplitude or frequency coding is alsoconceivable. These types of modulation also result in the advantageswith respect to the demodulation in the base station.

[0049] The coherence duration depends on the frequency differencebetween the base signal A and oscillator signal B, that is to say on thefrequency difference between the oscillator 2 and the base stationoscillator 7. The more precisely the frequencies of the oscillatorsagree, the longer it is that the phases of the oscillators are almostidentical. To increase the coherence duration and thus to be able tokeep the clock rate of the switching means 4 low, it may be advantageousto provide means which are suitable for adaptively adapting thefrequency of oscillation of the oscillator 2 to the frequency of thebase signal A. FIG. 4 shows a possible embodiment of this. Differentlyfrom the base circuit from FIG. 1, this device does not have afixed-frequency oscillator but a variable-frequency oscillator 14. Apart of the oscillator signal B of the variable-frequency oscillator 14is mixed with the base signal A by means of a mixer 15. The differentialmixed signal is extracted by means of a filter 16, preferably a low-passfilter. The frequency of the differential mixed signal which is ameasure of the frequency deviation of the two oscillators is then fed ascorrecting variable to a controller 18 following the signalpreprocessing 17. The controller 18 corrects the oscillator 14 in such amanner that the frequency deviation between the two oscillators 14, 7becomes as small as possible. The main task of the signal preprocessing17 consists in determining the frequency. In principle, the frequencydetermination can be carried out in any circuit or signal processor ofthe prior art. Similarly, the controller 18 can be designed inaccordance with the prior art. However, it should be pointed outexpressly that only the frequency needs to be controlled, the phasecoherence is obtained by the configuration of the device according tothe invention. A phase-locked loop can, therefore, be omitted. Since itis generally unnecessary to select the clock rate of the switching means4 to have a particularly low frequency, the controller 18 of theoscillator 14 also does not need to be especially precise. The limit fora small phase deviation of π/10, mentioned initially, is sufficient ifthe frequency deviation is ten times smaller than the clock frequency ofthe switching means 4.

[0050] In a numerical example: if the radio link is implemented at 24GHz and the oscillator 2, 14 of the transponder 9 is switched at 100MHz, the 24-GHz base station oscillator 7 and the 24-GHz oscillator 2,14 are allowed to deviate from one another by up to 10 MHz in frequency.After each switch-on of the oscillator 2, 14, it oscillatesquasi-phase-coherently with respect to the base signal A over 120periods in the coherence time of 5 ns, that is to say the maximumdeviation is π/10. After switching off and switching on again, another120 quasi-phase-coherent oscillations are obtained, etc. From the pointof view of information technology, the base signal A and the oscillatorsignal B are thus quasi-phase-coherent over a relatively long period.

[0051] When selecting the oscillator 2, 14, attention must be paid tothe fact that its building-up time should be short compared with thecoherence duration. For this reason, the quality factor of theoscillator 2, 14 should not be selected to be too large. With referenceto the aforementioned numerical example, this means, for example, for a24-GHz oscillator with, for example, a quality factor of 10, that itstarts to oscillate within about 400 ps which is distinctly shorter thanthe coherence duration of 5 ns. However, the quality factor should notbe designed to be too low either since low-quality oscillators usuallyhave high phase noise. As has already been explained above, however,high phase noise can unnecessarily shorten the coherence duration. Asuitable compromise must be made when selecting the oscillator 2, 14. Inthe microwave range, oscillators are usually designed as resonantcircuit. As can be seen from FIG. 5, such a resonant circuit consists ofa radio-frequency transistor 19 to provide amplification and a resonator20 or, respectively, band-pass filter. The resonator 20, for example, isan oscillating LC circuit or a dielectric structure. The circuit can beconstructed, for example, in microstrip or coplanar technology. If theoscillator is connected to an antenna 5, it is particularly suitable forthe principle described. The oscillator is switched, for example, by theamplifier 19 being switched on and off by means of the switching means4.

[0052] The invention is particularly suitable for microwave systems withoperating frequencies above 10 GHz since according to the current stateof the art, the possibilities for direct phase control of the carrierare restricted or, respectively, very complex and expensive.

[0053] It should be noted that the general coherence between base signaland oscillator is only limited by the phase noise of the oscillator 2,14 and of the base station oscillator 7. This is because, even if thefrequencies of the two oscillators are different, the phase relationshipbetween the signals still remains deterministic after the switching-onprocess, apart from the phase noise. In principle, all embodimentsmentioned in the present invention can therefore also be used withslower switching clocks, that is to say those coherence durations whichare only determined by the phase noise. In this case, the method onlyneeds to ensure that the temporal phase change obtained due to thefrequency difference between the two oscillators is taken intoconsideration or compensated for in the evaluation. For example, thiscan be done by means of additional mixers/demodulators on the hardwareside or by suitable frequency and phase evaluation on the software side.As has already been shown, this additional expenditure can beadvantageously avoided by the oscillator to be coupled being switched onand off with sufficient rapidity.

1. A device for generating an oscillator signal (B) based on a basesignal (A), comprising an oscillator (2, 14) for the active constructionof the oscillator signal (B) by means of oscillations, an input (1) forthe base signal (A), and an output (3) for the oscillator signal (B)generated, characterized in that the oscillator (2) can be excitedquasi-phase-coherently with respect to the base signal (A) by means ofthe base signal (A) for generating the oscillator signal (B).
 2. Thedevice as claimed in claim 1, characterized in that the device has aswitching means (4) for switching the quasi-phase-coherent exciteabilityof the oscillator (2).
 3. The device as claimed in claim 2,characterized in that the switching means (4) is constructed in such amanner that the oscillator (2) can be switched in a predeterminedsequence.
 4. The device as claimed in claim 3, characterized in that thetime between successive switching of the quasi-phase-coherentexciteability of the oscillator (2) is less than or equal to thecoherence duration.
 5. The device as claimed in at least one of thepreceding claims, characterized in that the device has a means (4) forswitching the oscillator (2) off.
 6. The device as claimed in at leastone of the preceding claims, characterized in that the device has means(5) for sending out the oscillator signal (B).
 7. The device as claimedin at least one of the preceding claims, characterized in that thedevice has a means (4, 13) for coding the oscillator signal (B).
 8. Thedevice as claimed in at least claims 3 and 7, characterized in that theswitching means is constructed as the means (4) for coding.
 9. Thedevice as claimed in at least claim 7, characterized in that the means(13) for coding is an additional modulation unit.
 10. The device asclaimed in at least one of the preceding claims, characterized in thatit has adapting means (15, 16, 17, 18) for adaptively adapting thefrequency of the oscillator (2) to the frequency of the base signal (A).11. The device as claimed in at least one of the preceding claims,characterized in that the oscillator (2) has a building-up time which isshort compared with the coherence duration.
 12. The device as claimed inat least one of the preceding claims, characterized in that theoscillator (2) can be excited by the fundamental mode and/or asubharmonic mode of the base signal (A).
 13. An arrangement with adevice as claimed in at least claim 3 and with a base station (6) forreceiving the oscillator signal (B), characterized in that the basestation (6) has a band-pass filter (12), the center frequency of whichapproximately corresponds to the clock rate.
 14. The arrangement with adevice as claimed in at least claim 3, and with a base station (6) forreceiving the oscillator signal (B), characterized in that the basestation (6) has means for eliminating the influence of the clock rate.15. A method for generating an oscillator signal (B) on the basis of abase signal (A), in which an oscillator (2) is excitedquasi-phase-coherently with respect to the base signal (A) by the basesignal (A), the oscillator (2) oscillates following the excitation, andthe oscillator (2) actively constructs an oscillator signal (B) due tothe oscillation.